Audio microphones are commonly used in a variety of consumer applications such as cellular telephones, digital audio recorders, personal computers and teleconferencing systems. In particular, lower-cost electret condenser microphones (ECM) are used in mass produced cost sensitive applications. An ECM microphone typically includes a film of electret material that is mounted in a small package having a sound port and electrical output terminals. The electret material is adhered to a diaphragm or makes up the diaphragm itself. Most ECM microphones also include a preamplifier that can be interfaced to an audio front-end amplifier within a target application such as a cell phone. Another type of microphone is a microelectro-mechanical Systems (MEMS) microphone, which can be implemented as a pressure sensitive diaphragm is etched directly onto an integrated circuit.
In applications where MEMS microphones are implemented in small form factor packages such as smartphones or tablet computers, an audio interface using a minimum number of pins is used. One such interface is a pulse code modulated interface (PCM) that produces a PCM signal having a pulse width or pulse density proportional to the audio signal sensed by the MEMS microphone. It is also the case small form factor applications are often low-power, battery operated device that are sensitive to power consumption. In order to maintain a long battery life, the power consumption of the MEMS microphone and its board level audio interface is minimized in order to conserve battery life.